The Lithuanian state, which developed as a monarchy in the thirteenth century, had been consolidated by Grand Duke Gediminas (c. 1315—1342), and was to reach the peak of its political power as an independent state in the second half of the fourteenth century. Under the government of the sons of Gediminas, Grand Duke Algirdas and his ally, Prince Kestutis of Trakai, Lithuanian rulers continued to defend their lands against the attacks of the Teutonic Order, which was harrying the western borders of Lithuania in order to unite its lands in Prussia with the Letto-Estonian territories held by the Livonian branch of the Order.
While Lithuania was defending its northern and western borders from Catholic crusaders, it took over a wide expanse of territory which stretched from its own original ethnic domains in Aukstatija (Upper Lithuania) and Zemaitija (Lower, that is north-western, Lithuania) towards what became known later as Belorussia and Ukraine, as far as Smolensk, Briansk and the Black Sea steppes. Military successes strengthened the despotic authority of the grand duke. Whilst the Lithuanians, members of the Baltic family of Indo-European peoples, resisted Christianity despite repeated attempts to convert them to it, the Ruslan population inhabiting the greater part of Lithuanian-controlled territory (not ethnic Lithuania but western Rus') had been Christians of the eastern rite for several centuries. In the fourteenth century the Lithuanian state used Rus'ian written culture in the ruler’s chancery, but in order to preserve its political identity the Lithuanian nobility remained unwilling to convert to eastern Christianity, even though such a prospect was considered.
Jogaila (Jagiello), son of Algirdas, became grand duke in 1377. Five years later he drove his uncle, Kestutis, from his domain and established himself as sole head of the grand duchy, taking power into his own hands. His first act was to seek an understanding with the Teutonic Order with which he concluded peace in 1382 at the unacceptable price of the surrender of Zemaitija. His second course of action was to effect a rapprochement with Moscow. In 1384 Jogaila sought a Muscovite alliance, arranged his marriage to the daughter of Dmitry Ivanovich Donskoi, and undertook to receive baptism in the eastern rite. However, these plans came to nought when a third way was offered him by the Polish nobility. This would involve Jogaila’s baptism in the Latin rite, his marriage to Queen Jadwiga and his coronation as king of Poland. Before Lithuania’s eyes spread the prospect of weakening the pressure from the Teutonic Order, initiating joint Lithuano-Polish efforts against the Tatars, and settling the disputed Lithuanian border in Galician Rus' which was occupied by Poland.
The personal union of the kingdom of Poland and the grand duchy of Lithuania was brought about by the Union of Krevo (1385). As patrimonial lord of Lithuania, when he became king of Poland Jogaila united his inheritance with Poland by the terms of this act. On the one hand the patrimonial and personal character of Jogaila’s power contrasted with the Polish crown’s established autonomy from the person of the king. On the other, Polish nobles who wished to interpret the Union as the annexation of Lithuania to the crown encountered resistance from the grand duke’s kinsmen and counsellors who defended the separateness of the Lithuanian state.
Jogaila accepted baptism in the Latin rite in Cracow, taking the name of Wladyslaw. As a young man of twenty-three or twenty-four, he married Jadwiga in 1386 when she was thirteen. The royal couple henceforth acted together in the most important political affairs. J adwiga was a figure of uncommon beauty and education, a person of deep religious sentiment who was endowed with diplomatic talents that became apparent over the years. She died giving birth to her only daughter in 1399. Wladyslaw II Jagiello came to Cracow with the experience of government gained by his dynasty over several generations and, above all, with personal skills tested in politics and war. He was to occupy the Polish throne for forty-eight years.
The collective baptism of the Lithuanian population carried out in 1387 under the personal guidance of King Wladyslaw began the conversion of the ethnically Lithuanian part of the grand duchy. At first there was compulsion from the authorities, followed by a feeling of obedience to ecclesiastical authority and of belonging to a wider Christendom. In 1387 a bishopric was established in Vilnius, a second following in Zemaitija in 1417. The numerical sparsity of the clergy, widely spread settlement and the powerful resistance put up by traditional culture meant that full acceptance of the new faith took several generations, embracing the upper social strata first. In addition to the Polish clergy, Lithuanian priests appeared early on. The leaders of the Lithuanian Church were educated at the University of Cracow which had been restored for this purpose, too, by Queen Jadwiga and King Wladyslaw.
The resistance of members of the Lithuanian dynasty to the Polish interpretation of the Union of Krevo led to opposition formulated by the king’s cousin, Vytautas (Vitold), son of Kestutis, who sought the support of the Teutonic Order. King Wladyslaw, however, worked out a compromise between the Lithuanian and Polish positions. In 1392 he made Vytautas co-ruler of Lithuania, adopting for a few years the higher title of dux supremus while Vytautas was styled magnus dux. Over the years Grand Duke Vytautas became King Wladyslaw’s partner, but conducted his own domestic and foreign policies. He consolidated the grand duchy by removing several of his kinsmen from their own princely domains and turning them into grand-ducal governors. He maintained his Volynian borders, too, despite the actions of Polish nobles. Vytautas sought to make the Golden Horde his dependant, but in 1399, on the banks of the river Vorskla (which flows into the Dnieper), he suffered a defeat which fixed for three centuries the line of the Tatar threat to the southern borders of Lithuania and Poland. At the same time this setback illustrated the indispensability of the alliance of the two nations if they were to maintain their international position.
After the death of Queen Jadwiga, Wladyslaw was acknowledged by the Polish nobility as king of Poland. This led to recognition of the equal political status of Lithuania and Poland by an act agreed by Wladyslaw and Vytautas in 1401.